Automotive vehicle cabin comfort is maintained by air conditioning systems which provide for heating, cooling and ventilation of cabin air. These systems are commonly referred to as HVAC systems. Originally, vehicle HVAC systems relied upon fresh air from outside of the passenger compartment for heating, cooling and ventilation. As conditioning systems developed, a recirculation mode was introduced to increase efficiencies. Accordingly, typical automotive vehicle HVAC systems have two air handling operating modes: a fresh air mode and a recirculation air mode.
Vehicle operators and passengers often select the air inlet mode of the conditioner without considering optimum performance of the system, including strain placed on vehicle components. For example, if the fresh air mode is selected as the source of air for the HVAC system in hot weather, the system compressor will experience a higher load. This can result in a high compressor discharge temperature and pressure that can lead to compressor or clutch damage or damage to other refrigerant components. In addition, engine coolant temperatures as well as engine and transmission oil temperatures can exceed recommended levels, which can degrade powertrain performance. On the other hand, there are factors that disfavor use of the recirculation mode under certain circumstances. For example, use of the recirculation mode under certain ambient conditions may cause cabin fogging.
It would be desirable to have an HVAC system in which the recirculation mode of a vehicle HVAC system is automatically selected under certain conditions to optimize cabin comfort and vehicle component life.